PC Motherboard Technology

The other motherboard we’ll examine is designed to support AMD Athlon and Duron processors. We chose this board for analysis because it is intended for higher-end applications and power-users. This is partly because of the support for DDR memory, but also because of the extra Asus features to support overclocking. Since the A7M266 is based on a combination AMD/VIA chipset, it makes a nice contrast to the Intel 815-based motherboard. We won’t go through an exhaustive list of features like we did for the Intel board, but there are some interesting differences that highlight concepts we’ve covered in this article. The board supports all of the newest features, such as AGP 4X, ATA-100, and 4 USB ports. Figure 6 shows the layout of this board.

Support for AMD Socket A Processor, 266 MHz FSB and a Big Heatsink

In the photograph in Figure 7, 7 notice the extra clearance around the processor socket. The cylindrical components are capacitors and help remove noise from the power supply signals. On the Asus board, the tall capacitors are located far enough away from the processor socket to allow an oversized heatsink and fan. The overclockers love this, since a cooler CPU tends to run faster than the rated speed (which assumes worst-case temperature). To help with thermal management, the Asus board has a temperature sensor located under the processor socket. This sensor is used to report the CPU temperature to the BIOS.

Special Asus Chip for Hardware Monitoring

One unique feature of most Asus boards is the Application Specific Integrated Circuit (ASIC) that Asus designed to monitor motherboard temperatures, voltages and fan speeds. Asus includes software that helps a user monitor these parameters. The BIOS could also be configured to bring up a warning message if any parameters get outside a user-defined tolerance.

AMD 760 North Bridge with a VIA VT82C686B South Bridge

Since the AMD 760 uses a PCI South Bridge connection, Asus was able to use a well-known VIA chip for the South Bridge. Each motherboard must have a special version of the BIOS customized for the features of the board. As this article has shown, most of the features live in the South Bridge. Using the VIA South Bridge instead of the new AMD South Bridge probably helped Asus simplify the task of porting the BIOS. As we’ve learned, there is a potential system bottleneck between the NB and SB, since the AMD chipset relies on PCI and doesn’t support a faster interconnect mechanism.

BIOS Allows 1 MHz Frequency Increments

If the Athlon/Duron processor has been modified to allow overclocking, then the Asus motherboard allows the FSB frequency to be adjusted in 1 MHz steps. Recall that the processor internal frequency is a multiple of the bus frequency. As an example, a 1.1 GHz Athlon would have an 11X multiplier and a 100 MHz bus. The fine granularity of the Asus frequency control may allow a stable configuration that gets a few more MHz of performance, though we urge caution. The Asus board also has a full set of jumpers, in case a user would prefer not to use the BIOS. However, jumper control of the bus frequency is much more limited than is possible using the BIOS.

Audio Modem Riser (AMR) Allows Low-Cost Audio or Modem

The 5th PCI slot is shared with a connector for AMR, similar to the way the Intel board used CNR for optional low-cost audio and telephony peripherals. As we described earlier, the new ACR (Advanced Communications Riser) card standard is a compatible upgrade of the older AMR connection used on this Asus board. For most users of this motherboard, it doesn’t really matter. Since this is a higher-end motherboard, most users will opt for the better performance of PCI audio cards. It’s also likely that home or business users won’t need an analog modem for day-to-day communication needs, since they usually connect to a LAN or a broadband Internet device (DSL or cable modem). But it’s still a good idea to equip desktop systems with analog modems for emergency communication purposes.. The Asus card supports an optional 3Com Ethernet chip on the motherboard.

Overall Conclusions About the A7M266

The only obvious architectural drawback of this board is the lack of a high-speed port between the North and South Bridge chips. This would only be a bottleneck if several high-speed peripherals were connected to the South Bridge. By using DDR memory and a fast AGP 4X graphics card, this motherboard appears to be well-suited to high-performance entertainment software. Check out the full reviews of the Asus board (and the Intel board) in the Motherboard Roundup.

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